The present invention relates generally to semiconductor fabrication and more specifically to maintaining wafer ID characters/laser marks on semiconductor wafers.
Semiconductor wafers are identified through the use of laser marks. However, after the wafer bumping process, the laser marks are obscured and are rendered not visible due to overlying bumps obscuring part of or all of one or more identifying letter/numbers. Thus the wafer laser marks can""t be subsequently read by optical character recognition (OCR) and causes scrapping of some of the wafers due to wrong wafer ink. That is if the solder bump wafer is defective, the wafer may be incorrectly recognized causing the wafer to be incorrectly inked with an identification number.
For example, as shown in FIG. 1, a wafer 10 may be identified with a wafer ID number with characters 12 such as xe2x80x9cG60539-2D8xe2x80x9d laser marked on the wafer 10 proximate a notch 14 used to determine the orientation of the wafer 10.
FIG. 2 is an enlarged portion of field 18 of FIG. 1 designated xe2x80x9cFIG. 2xe2x80x9d after a conventional bump process forming bumps 20. As shown in FIG. 2, the bumps 20 so formed, obscure the wafer ID characters 12 since the bumps 20 are indiscriminately formed over the wafer ID characters 12.
U.S. Pat. No. 6,121,111 to Jang et al. describes a process for removing metal from over the laser mark area.
U.S. Pat. No. 6,043,133 to Jang et al. describes a method of removing a shallow trench isolation (STI) oxide layer from over alignment marks.
U.S. Pat. No. 5,956,596 to Jang et al. describes a process to clean laser marks.
U.S. Pat. No. 5,401,691 to Caldwell describes an open frame for laser marks.
U.S. Pat. No. 6,277,658 B1 to Jeng et al. describes a method that uses a monitor wafer to monitor the shielding of metal over laser marks.
Accordingly, it is an object of one or more embodiments of the present invention to provide an improved method of making semiconductor wafer laser marks visible after bumping process.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a wafer having fields is provided. The wafer having at least one wafer identification character formed thereon within one or more of the fields. A dry film resist is formed over the wafer. Portions of the dry film resist are selectively exposed field by field using a mask whereby the mask is shifted over the one or more fields containing the at least one wafer identification character so that the one or more fields containing the at least one wafer identification character is double exposed after the mask shift so that all of the one or more fields containing the at least one wafer identification character is completely exposed. The selectively exposed dry film resist is developed to remove the non-exposed portions of the dry film resist. Solder is plated over the wafer exposed by the removed portions of the dry film resist to form solder bumps within the fields not containing at least one wafer identification character so that the at least one wafer identification character is readable by optical character recognition.